By investigations of phase relations in the alloy system Ba-Pt-Si at 900°C we observe the formation of the compound BaPtSi 3 , which crystallizes in the noncentrosymmetric BaNiSn 3 structure type. Its space group is I4mm with the tetragonal lattice parameters a = 0.44094͑2͒nm and c = 1.0013͑2͒nm for the arc-melted compound annealed at 900°C. The characterization of the physical properties of BaPtSi 3 reveals a superconducting transition at 2.25 K with an upper critical field at T =0 K of Ϸ0.05 T. For analyzing the electronic structure, density-functional theory calculations are performed yielding very good agreement between theory and experiment for the structural properties. From relativistic electronic-structure calculations, Fermi surface nesting features are found for two characteristic double sets of bands. The spin-orbit splitting of the relativistic electronic bands is in general rather small at Fermi energy and, therefore, superconductivity adheres to an almost undisturbed BCS state.

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In the present work we report on the synthesis, crystal structure, and physical properties (resistivity, magnetization, heat capacity) in combination with density functional theory (DFT) calculations of the electronic structure and phonon properties for the intermetallic compound LaPtSi. LaPtSi crystallizes in its own noncentrosymmetric structure type (space group I 4 1 md; a = 0.42502(1) nm and c = 1.4525(5) nm), which is an ordered ternary derivative of the centrosymmetric α-ThSi 2 -structure. The weakly correlated compound LaPtSi (Sommerfeld value γ = 6.5 mJ/molK 2 ) exhibits superconductivity below T c = 3.35 K and appears to be a fully gapped, weakly coupled s-wave BCS superconductor. The experimental observations are supported by DFT calculations which show that, despite a substantial spin-orbit splitting of the Fermi surfaces, a spin-singlet pairing is prevalent.

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